Method and system for filtering a speed signal in controlling a speed of a vehicle

Abstract

A method and a speed control system for controlling a speed of a vehicle utilizes a speed sensor for sensing a speed of the vehicle and generating a corresponding speed signal. A control unit determines one of a quick or slow acceleration status of the vehicle based on the speed signal. The control unit also determines a mode of operation of the speed control system and filters the speed signal based on the acceleration status and the mode of operation of the speed control system. The speed of the vehicle is then controlled based on the filtered speed signal.

What is claimed is: 
     
       1. A method for processing a speed signal for controlling a speed of a vehicle having a speed control system and a speedometer to eliminate driver perceived error between a desired target speed indicated on the speedometer and a target speed stored by the speed control system, the method comprising: sensing a speed of the vehicle and generating a corresponding speed signal;   determining an acceleration status of the vehicle based on the speed signal, the acceleration status being one of quick and slow;   determining a mode of operation of the speed control system, the mode of operation including set vehicle speed, accel, and coast modes;   filtering the speed signal based on the acceleration status and the mode of operation and generating a corresponding filtered speed signal to eliminate driver perceived error between the filtered speed signal and the speedometer; and   controlling the speed of the vehicle based on the filtered speed signal.   
     
     
       2. The method as recited in claim 1 wherein sensing the speed of the vehicle includes preliminarily filtering the speed signal to eliminate noise in the speed signal. 
     
     
       3. The method as recited in claim 2 wherein preliminarily filtering includes calculating a moving average of the speed signal. 
     
     
       4. The method as recited in claim 1 wherein filtering the speed signal includes filtering the speed signal according to one of a first set of filter coefficients and a second set of filter coefficients. 
     
     
       5. The method as recited in claim 4 wherein determining the mode of operation of the speed control system includes determining if a set vehicle speed is being selected by the speed control system and wherein filtering the speed signal includes filtering the speed signal according to the first set of filter coefficients upon determining a slow acceleration status. 
     
     
       6. The method as recited in claim 5 wherein the first set of filter coefficients is based on a first cut-off frequency. 
     
     
       7. The method as recited in claim 5 wherein filtering the speed signal includes filtering the speed signal according to the second set of filter coefficients upon determining a quick acceleration status and the set vehicle speed mode being selected by the speed control system. 
     
     
       8. The method as recited in claim 7 wherein the second set of filter coefficients is based on a second cut-off frequency, lower than the first cut-off frequency. 
     
     
       9. The method as recited in claim 1 further comprising: determining a desired speed of the vehicle according to the speed control system;   determining a current speed error between the desired speed and the filtered speed at a current sample interval;   determining a previous speed error between the desired speed of the vehicle and the filtered speed signal at a previous sample interval;   determining a difference between the current speed error and the previous speed error; and   comparing the difference with a predetermined threshold; and   limiting the current speed error if the difference exceeds the predetermined threshold to provide smooth transitions of the filtered speed signal during changes in operation mode or acceleration status.   
     
     
       10. The method as recited in claim 9 wherein controlling the speed of the vehicle includes controlling the speed based on the desired speed of the vehicle and one of the current speed error and the limited current speed error. 
     
     
       11. A speed control system for processing a speed signal for controlling a speed of a vehicle, the system comprising: a sensor for sensing a speed of the vehicle and generating a corresponding speed signal; and   a control unit operative to determine an acceleration status of the vehicle based on the speed signal, the acceleration status being one of quick and slow, determine a mode of operation of the speed control system, the mode of operation including a set vehicle speed, accel, and coast, filter the speed signal based on the acceleration status and the mode of operation to reduce driver perceived error between a vehicle speed indicated by a speedometer and a desired speed of the speed control system, and generate a corresponding filtered speed signal, and   control the speed of the vehicle based on the filtered speed signal.   
     
     
       12. The system as recited in claim 11 wherein the control unit is further operative to preliminarily filter the speed signal to eliminate noise in the speed signal. 
     
     
       13. The system as recited in claim 12 wherein the control unit, in preliminarily filtering the speed signal, is further operative to perform a moving average on the speed signal. 
     
     
       14. The system as recited in claim 11 wherein the control unit, in filtering the speed signal, is further operative to filter the speed signal according to one of a first set of filter coefficients and a second set of filter coefficients. 
     
     
       15. The system as recited in claim 14 wherein the control unit, in determining the mode of operation of the speed control system, is further operative to determine if a set vehicle speed is being selected and wherein, in filtering the speed signal, the control unit is further operative to filter the speed signal according to the first set of filter coefficients upon determining a slow acceleration status. 
     
     
       16. The system as recited in claim 15 wherein the first set of filter coefficients is based on a first cut-off frequency. 
     
     
       17. The system as recited in claim 15 wherein the control unit, in filtering the speed signal, is further operative to filter the speed signal according to the second set of filter coefficients upon determining a quick acceleration status and a set vehicle speed being selected. 
     
     
       18. The system as recited in claim 17 wherein the second set of filter coefficients is based on a second cut-off frequency, lower than the first cut-off frequency. 
     
     
       19. The system as recited in claim 11 wherein the control unit, in controlling the speed of the vehicle, is further operative to determine a desired vehicle speed, determine a current speed error between the desired speed and the filtered speed at a current sample interval, determine a previous speed error between the desired speed of the vehicle and the filtered speed signal at a previous sample interval, determine a difference between the current speed error and the previous speed error, compare the difference with a predetermined threshold, and limit the current speed error if the difference exceeds the predetermined threshold. 
     
     
       20. The system as recited in claim 19 wherein the control unit, in controlling the speed of the vehicle, is further operative to control the speed of the vehicle based on the desired speed of the vehicle and one of the current speed error and the limited current speed error. 
     
     
       21. A method for controlling speed of a vehicle to reduce driver perceived speed deviation from a desired target set speed displayed by a speedometer and a set speed used by a vehicle speed control system, the method comprising: filtering a vehicle speed signal using a first filter having a slow response when a command is received by the vehicle speed control system; and   filtering the vehicle speed signal using a second filter having a fast response to control the speed of the vehicle to the set speed after receiving the command to reduce driver perceived speed deviation between the speed corresponding to the command and the speed displayed by the speedometer.   
     
     
       22. The method of claim 21 further comprising: limiting speed error between subsequent samples to provide smooth transitions between use of the first and second filters.   
     
     
       23. A method for controlling speed of a vehicle to reduce driver perceived speed deviation from a desired target set speed displayed by a speedometer and a set speed used by a vehicle speed control system, the method comprising: determining acceleration of the vehicle;   filtering a vehicle speed signal using a first filter if the acceleration of the vehicle is below a predetermined threshold;   filtering the vehicle speed signal using a second filter otherwise; and   controlling speed of the vehicle based on the filtered speed signal.